The sensing of various conditions for indicating and control purposes is an old and highly developed technology. Typically, a condition sensor is mounted in an area where a condition is to be monitored and conductors then lead from that location to appropriate amplifiers and circuitry to interpret the state of the condition sensor. In the event that more than one condition is to be monitored, a plurality of condition sensors are provided and are individually connected through individual sensing channels or are selectively switched so that a single piece of amplifying or interpreting equipment can be used with the multiple sensors. The use of this type of technology requires a significant amount of interconnection wiring between the sensors and an output device responsive to the sensors.
In many installations, two conditions are sensed and used for indication and control purposes. More particularly, in residential environment control, the temperature and humidity of a controlled location are of importance. In winter time operation a heating plant normally responds both to a sensed temperature and the ambient is monitored for a proper humidity level. Normally when two conventional sensors for the humidity and temperature are mounted in a controlled environment, two sets of wires are required from the sensors to the control or indicating equipment. This redundant wiring adds significantly to the cost of an installation and to the equipment involved in the sensing and control of the ambient conditions.